Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$89.74	11.848%	$100.3724	$100.37	$100.35	$100.40
Purchase #2	$52.53	3.229%	$54.2262	$54.23	$54.25	$54.20
Purchase #3	$64.87	11.437%	$72.2892	$72.29	$72.30	$72.30
Purchase #4	$218.69	7.202%	$234.4401	$234.44	$234.45	$234.40
Purchase #5	$139.95	5.159%	$147.17	$147.17	$147.15	$147.20
Purchase #6	$160.72	6.194%	$170.675	$170.68	$170.70	$170.70
Purchase #7	$13.84	4.870%	$14.514	$14.51	$14.50	$14.50
7 purchase totals =	$740.34		$793.6869	$793.69	$793.70	$793.70